Fix: nasl builtin function recv timeout after first response

recv may return before length bytes have been read: as soon as at least one byte
has been received, the timeout is lowered to 1 second. If no data is received
during that time, the function returns the already read data; otherwise, if the
full initial timeout has not been reached, a 1 second timeout is re-armed and
the script tries to receive more data from the socket. This special feature was
implemented to get a good compromise between reliability and speed when
openvas-scanner talks to unknown or complex protocols. This functionality was missing.

rust/src/nasl/builtin/network/socket.rs

@@ -3,7 +3,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 use std::{
-    io::{BufRead, Read, Write},
+    io::{self, BufRead, Read, Write},
     sync::RwLock,
     thread::sleep,
     time::{Duration, SystemTime},
@@ -224,12 +224,17 @@ impl NaslSockets {
                 "the given socket FD {socket} does not exist"
             )))? {
             NaslSocket::Tcp(conn) => {
-                let mut pos = 0;
+                let mut pos = match convert_timeout(timeout) {
+                    Some(timeout) => conn.read_with_timeout(&mut data, timeout),
+                    None => conn.read(&mut data),
+                }?;
+                let timeout = Duration::from_secs(1);
                 while pos < min {
-                    pos += match convert_timeout(timeout) {
-                        Some(timeout) => conn.read_with_timeout(&mut data[pos..], timeout),
-                        None => conn.read(&mut data[pos..]),
-                    }?;
+                    match conn.read_with_timeout(&mut data[pos..], timeout) {
+                        Ok(n) => pos += n,
+                        Err(e) if e.kind() == io::ErrorKind::TimedOut => break,
+                        Err(e) => return Err(e.into()),
+                    }
                 }
                 Ok(NaslValue::Data(data[..pos].to_vec()))
             }